On Cycling Computers

posted Aug 16, 2009, 1:16 PM by Donald Vescio   [ updated Sep 12, 2011, 8:11 AM ]
I've some interesting contradictions--I'm very data driven when it comes to my training and racing, but I don't necessarily want to have detailed information displayed whent I'm actually on the bike.  During a training session, I'll track time and heart rate, mostly because I'm really interested on the impact that the session is having on my physiology.  HR data is less stochastic  (therefore less distracting as I concentrate on my workout) than power meter data, so I don't have to interpolate information as I ride.  Don't get me wrong--I do value power data and find it an excellent measure of whether I'm improving (or not) in my fitness.  I'll gather power data for regularly scheduled training sessions and for selected races; I'll also collect power data if I feel that something is not quite right with my training.

But for me, tracking heart rate is my constant, and I've used Polar's heart rate products for over twenty years.  They're solid and reliable, and the few times that I've needed it, their customer service was prompt and helpful.  I'm quite partial to Polar's CS600 bicycle computer/monitor, as it enables me to collect not only heart rate data, but also cadence, speed, and altitude data  as well.  I also can use the same computer to measure power, too, if I want (more on this in another entry).  Though its not based on the open ANT standard, Polar's wireless transmissions (called W.I.N.D. technology) is solid and I've never had any issues with a dropped signal or spiked reading.  I've even rigged up a simple wrist strap that enables me to use the CS600 indoors, if I want.

But Polar depends on a fork and wheel sensor for its speed and distance readings.  Though Polar's WIND sensors are small, they still require to be fastened on either the fork or chainstay, which will impact on aerodynamics.  Granted, the impact is minimal, but why have any at all, if it can be avoided?

Because I wanted as clean of an aerodynamic profile as possible on my TT bikes, I decided to try out Garmin's Edge 305.  Garmin's computer functions on an interesting concept in that it reads  GPS satellites for its data streams.  What this also offers to the user are additional data points, such as mapping and directional data; even better, for me, is that no speed sensors are required to collect speed and distance data.  The Edge's form and feature set are very good, and it's extremely easy to use; it offers two displays that can be customized by the user to include up to eight separate data fields each.

I used the Edge 305 for most of this season during both racing and training, and in all types of weather conditions. In general, I was fairly satisfied with its performance, though I noted that the data displayed for speed often lagged or was under-reported.  This was no big deal, as speed is not a data point that I track while riding, but it was noticeable. 

Three weeks ago, I started to have problems with the Edge.  For no explicable reason, the computer would suddenly shut down; at first, I thought that this was a random error, but the shut downs began to occur at more frequent intervals.  While I don't pay a lot attention to data while I'm riding, I do want consistent and accurate data tracks for post-session analysis--and the Edge suddenly was not reliable for this.

A little online research yielded a number of similar complaints from other users.  Apparently, the Edge 305 electronics are based on spring battery connections, which eventually fail over time.  During the normal course of riding, the bumps and jars experienced by the computer weaken these spring connections, causing the unit to shut down unexpectedly.  There are a number of interesting hacks to address this problem--the user forum on Garmin's own site documents the problem and the MTB Guru blog offers very detailed and illustrated instructions on how to fix the Edge's power issues.  Garmin is aware of the Edge's design flaw and offer users a replacement computer at a significantly discounted price if their specific units fail.

While many users most likely may never experience major problems with their Edge 305s, my experience reinforced the importance of relying on simple and familiar technology to collect my data.  I chose to experiment with the Garmin because it did not require remote speed sensors; I had absolutely no interest in its mapping or GPS capabilities.  Because I am not confident that I'll get an uninterrupted data stream, I've gone back to the Polar, which has proven its utility for the past several years. 

Edge 305 surgury, as documented on MTB Guru (see above)